Laboratory and epidemiological studies suggest that sleep loss may play a role in the increased prevalence of diabetes and obesity. The relationship among sleep restriction, weight gain, and diabetes risk may involve alterations in glucose metabolism, upregulation of appetite, and decreased energy expenditure. Shorter periods of sleep are associated with decreased glucose tolerance and increased concentrations of blood cortisol. Research has suggested that long-term sleep restriction (less than 6.5 hours per night) may cause a 40 percent fall in glucose tolerance.
An association between short, habitual sleep time and increased BMI has been reported in large populations. Short sleep was associated with changes in hormones that control hunger. Specifically, leptin levels were low while ghrelin levels were high. These effects were seen when sleep duration fell below eight hours. This suggests that sleep deprivation is a risk factor for obesity. One controlled study with healthy males found that a sleep time of around four hours was associated with significantly greater craving for calorie-dense foods with high carbohydrate content (sweets, salty foods, and starchy foods). Reported hunger was also higher.
One could also argue that less time spent sleeping would allow for more time for eating and drinking. This could certainly be a contributor to a general obesogenic environment. On the other side of the energy equation, sleep-deprived people are less likely to be physically active, resulting in lower energy expenditure. Taken together, the increases in appetite and food craving and decreases in activity create a compelling argument for understanding the role of sleep deprivation in weight management.